Human gene therapy is being actively considered as a possible treatment strategy for individuals with human immunodeficiency virus type 1 (HIV-1) infection or AIDS. There have been numerous gene therapeutic strategies proposed, including transdominant proteins, ribozymes and anti-sense RNAs, which have been utilized with variable success in the laboratory to block HIV-1 replication in culture. We have developed the severe combined immunodeficient (SCID) mouse as a model for both HIV-1 infection and pathogenesis and as an experimental system in which to investigate gene therapy approaches. The SCID mice can be transplanted with a human thymus (SCID-hu) which, in the presence of CD34+ progenitor cells, will give rise to mature CD4 + and CD8 + T-cells. We have shown that infection of these human transplants with HIV-1 results in pathology within three to four weeks, and we have shown more recently that stem cells can be transduced with vectors suitable for gene therapy purposes such that the mature T- cells also harbor the vector following differentiation. Although this model system is not perfectly representative of normal human hematopoiesis and/ or all aspects of HIV-1 infection, the combination of HIV-1 pathology and CD34+ progenitor cell transduction taking place within a relatively short period of time provides us with an experimental system in which to address many of the issues critical to successful gene therapy approaches for HIV-1 and AIDS. This application constitutes one part of a two-part interactive RO1 which aims to model gene therapy approaches for HIV-1 disease, utilizing the SCID-hu mouse. The accompanying application entitled, "Immune Reconstitution and Gene Transduction in the SCID-hu Mouse" (Jerome Zack, Principal Investigator) comprises the second part of this interactive RO1. That proposal aims to further develop the SCID-hu mouse and better understand the factors required for stem cell reconstitution and differentiation in the SCID mouse. This proposal focuses on vector testing and modelling specific gene therapy approaches using the SCID-hu mouse. The Specific Aims of this proposal are: 1. Optimize parameters for transduction of retroviral vectors into CD34+ stem cells and reconstitution in the SCID mouse. 2. Optimize parameters for transduction of adeno-associated virus vectors into CD34+ stem cells and reconstitution in the SCID mouse. 3. Test the feasibility of utilizing the SCID-hu mouse model to test selected gene therapy approaches. Since there are no known gene therapies that are currently successful for HIV-1, we will select two gene therapy approaches to model: a) transdominant; and b) RNA-based. We will determine the efficacy of various antiretroviral genes against HIV-1- induced pathology, based upon the results of Aim 3.